Field of the Invention
The present invention is related to systems and methods for percutaneous implantation of a heart valve prosthesis.
Background Art
Cardiac valves exhibit two types of pathologies: regurgitation and stenosis. Regurgitation is the more common of the two defects. Either defect can be treated by a surgical repair.
Under certain conditions, the cardiac valve must be replaced. Standard approaches to valve replacement require cutting open the patient's chest and heart to access the native valve. Such procedures are traumatic to the patient, require a long recovery time, and can result in life threatening complications. Therefore, many patients requiring cardiac valve replacement are deemed to pose too high a risk for open heart surgery due to age, health, or a variety of other factors. These patient risks associated with heart valve replacement are lessened by the emerging techniques for minimally invasive valve repair, but still many of those techniques require arresting the heart and passing the blood through a heart-lung machine.
Efforts have been focused on percutaneous transluminal delivery of replacement cardiac valves to solve the problems presented by traditional open heart surgery and minimally-invasive surgical methods. In such methods, a valve prosthesis is compacted for delivery in a catheter and then advanced, for example, through an opening in the femoral artery and through the descending aorta to the heart, where the prosthesis is then deployed in the aortic valve annulus.
Various types and configurations of valve prostheses are available for percutaneous valve replacement procedures, and continue to be refined. The actual shape and configuration of any particular valve prosthesis is dependent to some extent upon the native shape and size of the valve being repaired (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, valve prosthesis designs attempt to replicate the functions of the valve being replaced and thus will include valve leaflet-like structures. A typical percutaneous valve prosthesis includes a replacement valve that is mounted in some manner within an expandable stent frame to make a valved stent (or “valve prosthesis”). For many percutaneous delivery and implantation devices, the stent frame of the valved stent is made of a self-expanding material and construction. With these devices, the valved stent is crimped down to a desired size and held in that compressed arrangement within an outer sheath, also known as a capsule, for example. Retracting the sheath from the valved stent allows the stent to self-expand to a larger diameter, such as when the valved stent is in a desired position within a patient. In other percutaneous implantation devices, the valved stent can be initially provided in an expanded or uncrimped condition, then crimped or compressed on a balloon portion of catheter until it is as close to the diameter of the catheter as possible. Once delivered to the implantation site, the balloon is inflated to deploy the prosthesis. With either of these types of percutaneous stented valve prosthesis delivery devices, conventional sewing of the valve prosthesis to the patient's native tissue is typically not necessary.
It is imperative that the stented valve prosthesis be accurately located relative to the native annulus immediately prior to full deployment from the catheter as successful implantation requires the valve prosthesis intimately lodge and seal against the native annulus. If the prosthesis is incorrectly positioned relative to the native annulus, serious complications can result as the deployed device can leak and can even dislodge from the native valve implantation site.
While imaging technology can be employed as part of the implantation procedure to assist a clinician in better evaluating a location of the transcatheter valve prosthesis immediately prior to deployment, in many instances, this evaluation alone is insufficient. Instead, clinicians desire the ability to partially deploy the prosthesis, evaluate a position relative to the native annulus, and then reposition the prosthesis prior to full deployment if deemed necessary. Repositioning, in turn, requires the prosthesis first be re-compressed and re-located back within the outer delivery sheath. Stated otherwise, the partially deployed stented valve prosthesis must be “recaptured” by the delivery device, and in particular within the outer sheath. While, in theory, the recapturing of a partially deployed stented valve prosthesis is straight forward, in actual practice, the constraints presented by the implantation site and the stented heart valve itself render the technique exceedingly difficult.
For a self-expanding device, the stented heart valve is submerged in cold water in order to attach the stented heart valve onto the delivery system. This is because the shape memory material, typically Nitinol, is flexible at low temperatures. At warmer temperatures, for example inside the human body, the shape memory material becomes more rigid. In short, the stented heart valve is purposefully designed to rigidly resist collapsing forces once deployed to properly anchor itself in the anatomy of the heart. Thus, the delivery device component (e.g., outer delivery sheath) employed to force a partially-deployed segment of the prosthesis back to a collapsed arrangement must be capable of exerting a significant radial force. Conversely, however, the component cannot be overly rigid so as to avoid damaging the transcatheter heart valve as part of a recapturing procedure. Along these same lines, the aortic arch must be traversed, necessitating that the delivery device provide sufficient articulation attributes.
As mentioned above, an outer sheath or catheter is conventionally employed to deliver a self-deploying vascular stent. For the delivery of a self-deploying stented valve prosthesis, the high radial expansion force associated with the prosthesis is not problematic for complete deployment as the outer sheath is simply retracted in tension to allow the valve prosthesis to deploy. Were the conventional delivery device operated to only partially withdraw the outer sheath relative to the prosthesis, only the so-exposed distal region of the prosthetic would expand while the proximal region remained coupled to the delivery device. In theory, the outer sheath could simply be advanced distally to recapture the expanded region. Unfortunately, with conventional sheath configurations, attempting to compress the expanded region of the stented valve prosthesis by distally sliding the sheath is unlikely to be successful. The conventional delivery sheath cannot readily overcome the radial force of the expanded region of the prosthesis because, in effect, the sheath is placed into compression and will collapse due at least in part to the abrupt edge of the sheath being unable to cleanly slide over the expanded region of the prosthesis.